Ground triggered Latching Circuit using transistors

Discussion in 'General Electronics Chat' started by stillgrowingup, Feb 9, 2016.

  1. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
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    2
    Hi guys,

    I am at a complete loss. I have googled Latching transistor circuits and have only found diagrams using 12v Positive triggers, not a ground trigger. I am looking to build a latching circuit using NPN PNP transistors when pulsed by a N.O. switch to Ground.

    Requirements:
    Has to work with 12v DC to be used in my car.
    Circuit Latches when pulse to ground by N.O. switch. Unlatched when SAME N.O. switch is pressed to ground.
    Output from transistors need to offer Full Ground when active. Output will activate an 'On Board' 12v SPST Relay And send a Ground signal to illuminate a 12v Lamp 'OFF board'.
    No reset switch needed or will be used.
    Would like to have LED on board to light when circuit when circuit is active/Latched.

    I'm not looking for someone to the work for me. Hoping Someone here can point me in the right direction for answers or send a link that have answers. Doesn't even have use NPN PNP transistors. That just what I am thinking need to be used.

    Any feedback will be great and appreciated.

    TONY
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Post a schematic for one of the positive trigger latches you found. Might be as simple as adding an inverter before the trigger input.
     
  3. #12

    Expert

    Nov 30, 2010
    16,246
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    Das ist nicht ein latch. Das ist ein flippen-floppen. You've been looking for a one state circuit and you need a two state circuit. It might be called a bi-stable latch.

    This is the wrong one, but it's a start. It shows you need at least 2 transistors to achieve 2 stable states.
     
    Last edited: Feb 9, 2016
    cmartinez likes this.
  4. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    In all my Google searches .... This was always the first one listed in search results. Its missing the LED and Ground output to External/Off-board 12v Lamp.

    Here's the parts list for the schematic.

    R1, R2, R4 = 10K,
    R3 = 100K,
    T1 = BC547,
    T2 = BC557
    C1 = 1uF/25V
    D1 = 1N4007,
    Relay = As preferred.


    TONY
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Relay only flip flop?
    Single P.B.
    Max.
     
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    It's not push-on, push-off.
     
  7. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    I thought the 'INPUT trigger' was an External pulse to activate. So even though there is NO switch in the drawing. The input would've of received a pulse.

    If I am wrong, that's how lost I am on this. :)

    TONY
     
  8. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    Yes single Push button, N.O. sends ground to this circuit. The way I imagine this working is .....

    Ground pulse in. Activates transistors. Out from main controlling transistor will energize 12v Relay coil AND activates on board LED. I believe a third transistor will be needed to send Ground output to OFF-Board external 12v Lamp. This Third transistor will also be activated by Main controlling transistor.

    Am I making sense? ... I have an idea of where I want to go, but have no map to take me there. :(

    TONY
     
  9. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    Using the Term 'Flip Flop' that you guys said to me. I found this schematic. It seems almost what I'm looking for, correct?

    TONY
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
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    So the relay version won't work?
    You mention relay output.
    Max.
     
  11. crutschow

    Expert

    Mar 14, 2008
    12,969
    3,219
    The last circuit in my write-up may work for you, which uses the same wire for the push-button and the indicator.
    The indicators are LEDs if that's okay.
     
  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,758
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    I don't think that linked circuit in post #9 will work for you. Simulation shows it doesn't toggle. Even if the circuit could toggle, the LED would draw>40mA. It's what you might call a flop circuit ;).
     
  13. hp1729

    Well-Known Member

    Nov 23, 2015
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    Low in turns something on is no problem. What kind of "latching do you need? Transistor? Relay? How mucg current?
     
  14. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    This circuit I need is for energizing a relay. This relay is for controlling power to other devices in my car and will not exceed 10A. Exampl of items I may want to control are .... Head lamps, Parking Lights, Radio, heat seats, etc....


    Figures, my life would be too easy if it did. LOL


    Hi Crutschow, thanks for your help in my previous post. That circuit is up and running fine. :)

    The switches I will be using have 12v incandescent light bulbs. I definitely need separate input ground trigger and with separate Ground output to illuminate the 12v incandescent light bulb.

    TONY
     
  15. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    Will this be a Latching circuit? Circuit will maintain on until pulsed with ground again?

    TONY
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Ref PDF.
    That is all this does???
    Max.
     
  17. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    Will it be Latching though? Controlled on/off by a ground pulse? ... I've never worked with Pull up/down resistors.


    I found and attached yet another drawing. Seems to work with a Positive pulse and 5v DC though.

    S1 would be external. Not on board.
     
  18. hp1729

    Well-Known Member

    Nov 23, 2015
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    Latching version.
    Easily adapted to a relay if you want. It just turns on LEDs at this point. It defaults to "Reset" state on power on. You wanted transistors only? Only two PNP transistors required. Untested so far. But in theory it should work.
     
  19. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    I see 2 switches. How about just a single push on / push off. No reset.

    Thanks for ideas guys. This is great. Keep em coming :)
     
  20. hp1729

    Well-Known Member

    Nov 23, 2015
    1,935
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    Do you have a limit on how many transistors get used before you go to using an IC?
     
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